Orthodontic therapy is a specialty of dentistry that involves diagnosis and treatment of a malocclusion (or improper bite) to reposition teeth to proper locations in the oral cavity. Orthodontic therapy often enhances the aesthetic appearance of the teeth, especially in instances when the patient's front teeth are crooked. Orthodontic treatment can also improve the patient's bite, or occlusion, so that the upper and lower teeth are better coordinated with each other when the patient is chewing.
A common type of orthodontic treatment involves a set of intraoral appliances that are often collectively called “braces”. In this type of treatment, slotted appliances called brackets are initially bonded to the patient's anterior, cuspid and bicuspid teeth and tubular appliances called buccal tubes are bonded to the patient's molar teeth. After bonding these appliances to the teeth, a resilient appliance called an archwire is secured in the slot of each bracket, and the ends of the archwire anchored in the buccal tubes. During treatment, the archwire imparts forces to the teeth and also forms a track thereby guiding movement of the teeth to desired positions.
Many orthodontic brackets have lugs known as “tiewings” that are connected to a body of the bracket. Once the bracket has been attached to a tooth and an archwire has been placed in the archwire slot of the bracket, a ligature is coupled to the bracket with assistance of these tiewings to retain the archwire in the archwire slot. One example of a commercially available orthodontic ligature is a small, elastomeric O-ring that is installed by stretching the O-ring along a path behind the tiewings and over the facial side of the archwire.
Other types of orthodontic appliances called self-ligating appliances have a latch for coupling the archwire to the bracket. Use of the latch conveniently avoids the need to use ligatures to secure the archwire to the appliance. The latch may comprise a movable clip, spring member, sliding cover, shutter, bail or other structure that is connected to the appliance body for retaining the archwire in the archwire slot. Compared with traditional ligated appliances, self-ligating appliances can reduce friction between the archwire and the archwire slot during treatment, which can be advantageous in facilitating tooth movement.
Examples of improved, self-ligating orthodontic appliances with clips are described in U.S. Pat. No. 6,582,226 (Jordan et al.), U.S. Pat. No. 7,140,876 (Cinader et al.), U.S. Pat. No. 7,217,125 (Lai et al.), U.S. Pat. No. 7,377,777 (Lai et al.), and PCT Publication No. WO2010/014518 (Lai et al.). The appliances described in those documents have one or more clips for retaining an archwire in the archwire slot, and the clips release the archwire from the archwire slot whenever the archwire exerts a force on the appliance that exceeds a certain minimum value. The minimum value is significantly less than the force required in the same direction to debond the appliance from the tooth, and consequently helps to ensure that the appliance will not spontaneously debond from the tooth during the course of treatment.